The bandwidth that a single link has means that the maximum resolution for a single link DVI connection is 1900x1200. So for larger resolutions (link a 30") you need a dual link connection. Note that this does not mean that there are twice as many pins, two cables or that one link carries the top half of the screen and the other the bottom. There are two TDMS transceivers at both ends and they send at the same time, but out of sequence so as they don't interfere. So the top of the screen gets sent by both links at the same time resulting in twice the bandwidth

Not sure about the Apple screen but there have been reports of the Dell and HP screens refusing to work at all unless fed a dual link signal, probably because it's cheaper to build them without the logic required to ignore one TDMS transceiver to run in single link mode. I'd imagine the Apple display works the same way.

And really if you are going to run it at single-link resolutions you'd be better off buying a 24" screen if you are sitting close to it as the low resolution on the 30" will look terrible, or a 30" LCD TV (1080p) if you are sitting further away as it's cheaper.

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